One new and specialized type of imaging involves the capture of low intensity light—often on the order of only tens to hundreds of photons—from a light emitting sample. The source of the light indicates portions of the sample, such as traced molecules in a particular portion of a laboratory mammal, where an activity of interest may be taking place. For example, specialized in-vivo imaging applications may include analysis of one or more representations of emissions from internal portions of a specimen superimposed on a photographic representation of the specimen. The luminescence representation indicates portions of the specimen where an activity of interest may be taking place. The photographic representation provides the user with a pictorial reference of the specimen. Such imaging applications present numerous challenges.
One particular obstacle for these imaging systems is the diverse image capture conditions that they are required to perform under. Photographic image capture typically requires the sample to be fully illuminated. Luminescent image capture requires substantially no light, other than minute amounts produced within the sample. The accuracy of image capture at these low light levels is often inconsistent with conventional imaging systems. For example, inconsistency between different camera designs may affect the accuracy between different imaging systems. Alternately, drift introduced in the readout of a camera over its operational life may introduce inaccuracies that affect the repeatability of imaging within the same system over time. Irregularities between image capture trials on the order of several photons may contaminate data; thereby compromising the ability for an imaging system to provide absolute and repeatable results.
Since the cameras employ considerable sensitivity at low light levels, conventional techniques for calibration often produce too much light, saturate the cameras, and are unsuitable. In view of the foregoing, techniques for calibrating a low-level light imaging system would be desirable.